In information technology, high-frequency, sine-shaped or cosine-shaped carrier signals are generally utilized so as to be able to transmit information such as language, music, images or data. To this end, the message to be transmitted is modulated onto a carrier signal. Available modulation methods are the angle and amplitude modulation. In amplitude modulation the information contained in the message signal m(t) is modulated onto the carrier signal essentially according to the equation
s(t)=(a0+c·m(t))·sin(2πf0t), where f0 denotes the carrier frequency, and a0 and c are constants that are selected according to the practical requirements. A characteristic property of amplitude modulation is that the amplitude of the signal s(t) is modulated in the rhythm of message m(t) to be transmitted, frequency f0 of the modulated carrier signal not being able to be varied over time.
In the available angle modulation, the frequency or the phase is varied over time in the rhythm of the message signal m(t) to be transmitted. The frequency-modulated signal transmitted via a transmission channel is
s(t)=a0·sin (2{circumflex over (π)}f(m(t))), where frequency f(m(t)) in most cases being defined by the expression (f0+c m(t)). In a frequency modulation amplitude a0 is constant.